-What are the broad findings of this study? What is new or different?
-Will these findings accelerate the pace of sustainable housing adoption?
-Given this fresh review, what new challenges and hopes are identified?
-How did the research team coalesce around this project?
-What perspective and expertise do the team members bring?
The American lifestyle causes a disproportionately large share of damage to natural ecosystems, and a significant contributor to climate emissions comes from the housing sector. Addressing the operational energy footprint from residential housing would reduce greenhouse gas emissions in the U.S. by a third, and by more than half–on average–if onsite renewable energy also powers household transportation. The starting point for progress needs to include clean and renewable energy, and a viable choice today is distributed solar in active photovoltaic (PV) systems. Then, the simple inclusion or exclusion of onsite solar alters many of the choices in building materials and operational systems in surprising and counter-conventional ways.
The combination of improved technologies, recent price reduction below critical thresholds, and more accommodating regulatory environments have changed the game on home solar PV installations. In nearly every area of the country today, solar PV is not only a good choice environmentally, but it is also a strong financial investment, with higher returns than what might be expected from a diversified portfolio in U.S. equity markets. Unfortunately, this is difficult to both understand intuitively, and to communicate, because the financial model for solar PV requires a significant and known initial cost, while a predicted set of benefits accrue over many years.
With onsite solar PV both economically and environmentally advantageous, it sets up three different scenarios for building the most sustainable house possible from a combination of embodied and operational energy. These are listed in the accompanying charts.
Solar PV Available and Ready – SOAR Home
Solar PV is fully available within local utility and regulatory environments and with adequate onsite mounting space to generate all of the annual energy demand of the home and transportation.
Solar PV Ready, but with Tempered Availability – SORTA Home
Solar PV is available, but limited in some way. This could be from limits to a potential capture area for sunlight (roof too small or partially shaded), or limitations by local utility or regulation.
Solar PV Not Available – SNAIL Home
Solar PV is simply not available in any size or capacity; an example might be a home that does not have a suitable mounting area, or where local utility or regulation blocks access.
What classification is your home in?
for all homes
- Eliminate direct use of fossil fuels in favor of 100% electric equipment and appliances. When fossil fuels are burned, the emissions pollute locally and contribute to climate change globally. Grid-distributed electricity in the U.S. is still generated with a mix of fossil fuels, and these are slowly being displaced by cleaner and renewable energies. Where on-site solar PV is possible, electricity is the preferred energy medium.
- When designing for new construction, spaces and rooms should be sized for practical need. This should use fewer dollar and environmental resources to build and require less energy to operate. Working with an architect may help make spaces functional and right-sized in the design phase.
- Orient the building to allow for maximum solar gain to the south (in northern hemisphere locations) and, to the extent practical, buffer the building to the north and northwest; this is more important in colder climates with a high number of heating days.
- The first priority in design should be to provide for adequate solar PV gain; this will include sufficient space for an array of panels, orientation (azimuth) to the south, and location-dependent angle (pitch). Passive heat gain may also be considered in design.
- Aim to produce as much renewable energy on-site as is possible or practical, up to 100% of the annual energy needs of the home and private transportation. If space and regulation permit, size PV to produce a surplus that can offset the embodied energy of the building.
The building code is a set of rules and requirements that set minimum standards for building structure and insulation. The purpose of the building code is to protect health, safety, and general welfare in the construction and occupancy of buildings. Most local building codes are adapted from the International Building Code and the International Residential Building Code. They set standards for wind loads, snow loads, occupancy, fire safety and other aspects that ensure minimum levels of safety and energy use.
Scenarios and Criteria
Cost to build and equip
Overall environmental impact
Available to who?
Code-minimum with quality and integrity
Basic and simple
Size solar PV for 100% of annual household energy needs plus EV transportation, then build a code-minimum house with quality construction to ensure integrity and longevity.
Weak link upgrades only to PV limit
Plan to maximize solar PV within site limitations, then select building envelope upgrades at the weakest links with the goal of reducing energy needs to within onsite power production limits.
Weakest link upgrades (up to windows and doors)
Consider a different site that accommodates solar PV; otherwise, target recommended envelope upgrades, starting with the weakest links and a non-sustainable overall outcome.
This analysis uncovered two enormous surprises and one big irony. The first surprise is that recent improvements in solar technology and cost make residential PV installations not only viable, but financially lucrative. The second surprise is that many upgrades to the building envelope, historically done in the interest of environmental responsibility, actually return relatively small environmental benefits that are most often outweighed by environmental harms. Conventional wisdom has everyone thinking that the first step is reducing energy demand, and then add solar as a secondary step. Unfortunately, very few homeowners can afford the investments needed to achieve energy savings from building envelope upgrades, and they never get to the solar step; most also do not understand the true costs (and overall benefits) of onsite solar. The outcome is predictable; almost no progress in reducing harmful environmental impacts from the residential sector.
We need to think of onsite solar as the first priority rather than the afterthought. When household energy use is met by onsite production of cleaner and cheaper solar energy, suddenly the building envelope becomes much less important. Every dollar invested in solar PV has direct, known, and significant impact in reducing environmental harm, at least when displacing fossil fuel-derived energy. That claim cannot be made for any building envelope upgrade, most of which have negative financial return and net negative environmental impact.
The enormous irony is that the answer has been right in front of us, yet seemingly elusive. Because our decisions are too often driven by short term knowledge or interests (immediate costs) without a full understanding of longer term results, we’ve missed the integrated and life-cycle whole. Our focus on the trees in front of us veiled the trees behind and the forest as a whole. In our research we demonstrate that the most responsible environmental choice in most U.S. housing markets is the basic, least-costly, code-minimum house with solar PV providing annual energy needs. Our analysis firmly suggests that the most responsible choice environmentally happens to be the least costly option, not only initially at construction, but operationally through its life cycle and at decommissioning. Another irony is that environmental interests in the industry still advocate robust, premium building envelopes and this, unfortunately, limits action to the wealthy few and drives a belief that nothing meaningful can be achieved except with enormous financial investments.
-Learn of onsite solar PV capacity before site selection with the aim of finding a site that accommodates sufficient onsite renewable energy generation for household energy and ideally for EV transportation.
-Consider adding solar PV to existing structures as priority before envelope upgrades.
-Don’t build new housing where solar PV is not available, or where it is too limited.
-Don’t assume the most energy efficient option is always the best environmental choice.
-Don’t assume that building (or living in) a sustainable home is more expensive; it is not!
-Don’t compromise the richness of history and culture in existing homes with invasive renovations if solar PV is available.